CBO Access Path

Access Paths are ways in which data is retrieved from the database.

FTS:All adjacent blocks under the HWM are sequentially scanned.Use large I/O calls(DB_FILE_MULTIBLOCK_READ_COUNT).

The CBO choose FTS under the following situation:

1.lack of index

2.a large mount of data

3.small table: if a table contains less than DB_FILE_MULTIBLOCK_READ_COUNT blocks under the HWM.

4.high degree of parallelism: DEGREE column in the ALL_TABLES.

5.FTS hints /*+ FULL(table alias) */

困了,睡觉去了,明天再总结^^